1. Field of the Invention
The present invention relates to a method of forming a conductor path, more particularly, to a method of forming a conductor path which is formed on an insulating substrate by selective heat-treatment and has good conductivity.
2. Description of the Prior Art
The formation of a conductor path is important for organically coupling electrical parts formed on a circuit substrate and manufacturing complicated electrical devices. Conventionally, such a conductor path is formed by using a copper wire, or a copper foil layer is formed on a printed circuit board. A method is known in which a so-called conductor paste, formed of a mixture containing a metallic powder and an insulation matrix material, is used to form such a conductor path.
However, in these conventional methods, a conductor path cannot be directly connected with electrical parts. In order to connect the conductor path to the electrical parts, solder is used, or a wire of gold, copper, aluminum or the like is bonded. For this reason, disconnection of the solder or the bonding wire causes degradation of reliability of the electrical devices, and a device size becomes large by the use of the solder or the bonding wire. Therefore, these disadvantages prevent a satisfactory electronic circuit configuration from being achieved.
In accordance with current demand for compact and light-weight electronic devices, a circuit in the device needs to be highly integrated, and therefore, micro-patterning of the wiring pattern is needed. However, since screen printing is performed in a current thick film circuit technique, micropatterning of a screen mask and the particle size of a metallic powder in a conductor paste are greatly limited, and a wiring width is practically limited to 100 .mu.m. In addition, a wiring pattern is limited to a pattern of a mask. When a circuit design is changed, the mask design must be also changed. On the other hand, a thin metal film may be formed by vapour deposition, and etched to form a conductor circuit. However, a manufacturing process of this method is complicated, and a batch technique must be used, resulting in poor profitability.
In Japanese Patent Disclosure (Kokai) No. 55-14801 and No. 58-12392, a method is disclosed in which an insulating polymer is locally heated and a heated portion is carbonized to form a conductor path such as a resistor. However, in this method, since the obtained conductor path consists of carbon, the conductivity thereof is lower than that of a metal, and it has poor mechanical strength.